1. By using the teleconverter, will I loose one F stop or does it remains the same?
For exposure purposes, a 2x TC takes two stops, a 1.4x takes 1 stop, and the 1.7x takes 1.5 stops. If you are using TTL metering, the camera automatically adjusts for the teleconverter.
2. If I use the A series teleconverters on an AF body, do I still have the AF ability or do I go MF?
Pentax doesn't make a TC that couples the camera's AF drive to the lens, so you will have to go MF. The 1.7x AF adapter achieves auto focus by linking the elements in the TC to the camera's AF. It's not as good as the AF on the lens itself, but provides some AF capabilties with both AF and MF lenses.
3. Among the TCs, is there any specific one that you guys favour?
When you use a teleconverter, you are combining two optical systems - the lens and the TC. Unless you are using pieces that were designed to work together, it really is a crap shoot. In terms of third party teleconverters, I've had the Vivitar macro focusing TC, a Tamron 7 element 2x TC, and a Kiron TC 2x 7 element. Some work well with some lenses, less well with others. There are plenty of bad TC's out there, but in regards to the good ones, some work better with certain lenses than others.
- MCC
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Mark Cassino Photography
Kalamazoo, MI
http://www.markcassino.com
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